For permit applications submitted on or after January 1, 2026, the 2025 California Energy Code is the starting point. Your approved CF1R documents and window schedule—not a generic brochure—should control the final order.
We understand why this feels confusing. You may have a beautiful set of elevations, a favorite slim-frame window, and a supplier promising “California compliant.”
Then an energy consultant starts asking for U-Factor, SHGC, NFRC data, west-facing glass area, and climate-zone information. Suddenly, what looked like a design decision feels like an exam.
It does not need to be that way. The practical goal is to connect the numbers to the way you want to live: a comfortable sofa beside the glass, a kitchen that does not overheat in the afternoon, and sliding doors that open the house to the terrace without creating an energy-code problem.
Title 24 Window and Door Terms Explained
“Title 24” is often used as shorthand for California’s building requirements. For energy performance, the relevant document is Title 24, Part 6—the California Energy Code. The 2025 edition took effect on January 1, 2026, and applies to new buildings as well as applicable additions and alterations.
| Term | Plain-English meaning | Why it matters to your home |
|---|---|---|
| U-Factor | How readily heat passes through the complete product. Lower is generally better. | Affects winter heat loss, air-conditioning demand, and how comfortable you feel near the glass. |
| SHGC | Solar Heat Gain Coefficient: the share of solar heat admitted through the product. Lower values block more solar heat. | Especially important for hot inland areas, large openings, and glass exposed to afternoon sun. |
| Low-E glass | Glass with a microscopically thin low-emissivity coating that manages radiant heat. | Helps achieve the target U-Factor and SHGC, but “Low-E” alone is not a compliance rating. |
| VT | Visible Transmittance: how much daylight passes through. Higher values admit more visible light. | Influences brightness, glass color, glare, privacy, and how natural finishes look indoors. |
| NFRC rating | An independent whole-product energy rating for windows, doors, and skylights. | Lets the design team compare the frame, glass, spacer, and operating type as one tested or simulated system. |
| Prescriptive path | The project follows the listed component limits and allowances. | Simple to understand, but it can restrict glass area or certain product values. |
| Performance path | Approved energy software evaluates the home as a complete design. | May provide flexibility for luxury homes with large glass areas when other features compensate. |
The most common misunderstanding is comparing center-of-glass data with the required whole-product value. A very efficient insulated glass unit can still produce a weaker overall result when placed in a highly conductive frame or a large operable system. Ask for the value covering the actual assembly—not an attractive number taken from the glass supplier’s data sheet.
How California Climate Zones Affect Window Performance
California uses 16 building climate zones. This is not a formality. The California Energy Commission (CEC) explains that envelope and fenestration requirements vary by the project’s physical location. A cool, foggy coastal site and a sun-exposed desert property should not receive the same glass recipe simply because both have a California address.
Start with the address, not the nearest famous city
Use the CEC Climate Zone Tool with the exact site address or ZIP code. Some ZIP codes cross climate-zone boundaries, so the project team should verify the local jurisdiction’s determination. We recommend putting the confirmed zone on the window schedule and in the supplier’s quotation notes. That one line prevents a surprising number of later questions.
Coastal homes often prioritize balanced daylight, ventilation, salt-resistant hardware, and large indoor-outdoor openings. Hot inland and desert homes usually need tighter control of solar gain, especially on west-facing walls.
Mountain and colder inland locations place more emphasis on insulation, air tightness, and reducing the cold sensation near large panes. Those are design priorities; they do not replace the project’s calculated code values.
Prescriptive reference values for new single-family homes
| 2025 Energy Code climate-zone group | Maximum window U-Factor | Maximum SHGC | Design reading |
|---|---|---|---|
| Zones 1–5, 11–14 and 16 | 0.27 | Varies: 0.23 or not required by zone | Lower U-Factor is emphasized in many coastal, inland, and mountain locations. |
| Zones 6–10 | 0.30 | 0.23 where prescribed | Solar control, orientation, and opening area remain important. |
| Zone 15 | 0.30 | 0.20 | The hot desert zone has the most restrictive prescriptive SHGC listed for new homes. |
| Zones 1, 3, 5 and 16 | Use applicable value above | N/R | “Not required” does not mean solar comfort, glare, or HVAC loads can be ignored. |
Under the prescriptive approach, the current CF1R instructions calculate total fenestration allowance at 20% of conditioned floor area. They also apply a 5% west-facing allowance in Climate Zones 2, 4, and 6–16. A glass-heavy luxury home is not automatically impossible.
It may simply need thoughtful orientation, exterior shading, better-performing assemblies, or a whole-building performance calculation.
U-Factor, SHGC and Low-E Glass—What Should You Choose?
There is no universal “best glass.” The right specification manages four things at once: heat transfer, solar gain, useful daylight, and appearance. Push one number to an extreme and another part of the experience may suffer.
Use U-Factor to protect comfort, not only the energy model
A lower U-Factor slows heat flow through the complete window. That is valuable in colder climate zones, but it also matters in air-conditioned homes because it reduces heat transfer from outside.
For a large picture window beside a bed or reading chair, improved thermal performance can make the space feel noticeably more comfortable. With aluminum systems, we normally look for a genuine thermal break, suitable insulated glazing, and careful perimeter installation—not merely a thicker profile.
Match SHGC to sun exposure and daily life
SHGC tells us how much solar heat comes through. A lower value can help a hot, west-facing living room, yet blindly choosing the darkest, lowest-SHGC glass can flatten daylight and alter exterior color. Before we recommend a coating, we ask simple questions: Which rooms receive afternoon sun? Is there a deep roof overhang? Will trees or neighboring buildings shade the glass? Do the owners want bright neutral daylight or a more tinted appearance?
This is where architecture earns its keep. A well-sized overhang can stop high summer sun while preserving views. A recessed opening may improve comfort without making the glass look dark. If cold-weather performance is your concern, our guide to buying windows for cold-climate homes explains the frame and glazing details worth discussing.
Low-E is a tool, not a finished specification
Low-E coatings can be tuned for different performance goals, and coating surfaces within an insulated glass unit matter. The final selection should state the glass build-up, pane thicknesses, air or gas space, safety treatment, coating, spacer, and whole-product ratings. For oversized doors, structural requirements and safety glazing may influence the build-up before the energy numbers are finalized.
Designing and Specifying Windows and Doors for a California Home
Beautiful openings begin with the way a room will be used. A fixed picture window can deliver slim sightlines and strong thermal performance, but it does not ventilate. Casement and awning windows can seal tightly and catch breezes.
Sliding systems save space and create wide openings, yet their panel size, track design, air leakage, water performance, and threshold need careful coordination.
For a whole-home package, we try to establish a visual family: consistent frame depth, mullion proportions, finish, handle style, and glass color.
You can review our main custom windows and doors options, including thermally broken aluminum windows and large-format sliding door systems. The architectural language should feel consistent even when the operating types change from room to room.
What belongs on the window and door schedule?
A useful schedule should identify every opening by tag and include location, rough opening or unit size, operating type, orientation, frame material and finish, glazing build-up, Low-E coating, U-Factor, SHGC, safety-glazing status, insect screen, hardware, and installation condition.
Add structural design pressure, water testing criteria, egress, fall protection, wildfire requirements, and accessibility information where applicable.
The CEC’s CF1R instructions say that glazed doors with at least 25% glass are treated as fenestration. This matters for full-height entry doors, patio sliders, and pocket doors: they cannot quietly disappear from the energy calculation just because the schedule labels them “doors.”
Can imported windows satisfy Title 24?
Yes—country of manufacture is not the deciding factor. The exact proposed system must have acceptable performance documentation, match the approved schedule, and satisfy the project’s other applicable requirements.
For custom products manufactured in China, we coordinate dimensions, frame series, glass build-up, finish samples, Shop Drawings, packaging, and logistics. But we will not tell an owner that every custom size is compliant just because one catalog sample has a good number.
Before production, compare the NFRC-certified configuration or accepted rating source with the actual frame type, operator, glass, grid, spacer, and size range. The National Fenestration Rating Council explains that its label reports whole-product U-Factor, SHGC, VT, and air leakage. That is much more useful than a glass-only certificate.
Title 24 Pre-Order Checklist
This is the checklist we would want beside us before approving a deposit or releasing a custom order:
- ✓Confirm the exact project address and CEC climate zone.
- ✓Confirm which Energy Code edition applies to the permit.
- ✓Classify the work as new construction, addition, or alteration.
- ✓Ask whether the project uses the prescriptive or performance path.
- ✓Obtain whole-product U-Factor and SHGC data for each relevant system.
- ✓Check glass area and orientation, including west-facing openings.
- ✓Include glazed entry and sliding doors in the fenestration review.
- ✓Match window tags across elevations, schedule, quotation, and Shop Drawings.
- ✓Check safety, egress, wildfire, structural, water, and installation requirements separately.
- ✓Keep temporary labels in place until the building inspector verifies them.
- ✓Confirm the CF1R values before production and the CF2R installation responsibilities before delivery.
- ✓Get final approval from the California architect, energy consultant, and authority having jurisdiction.
A practical tip: freeze the performance values and appearance together. If the architect approves a clear neutral glass sample but purchasing later substitutes another Low-E coating to improve SHGC, the home may arrive with a different color and reflectivity. Compliance, quotation, and finish approval should all reference the same final glass code.
Frequently Asked Questions
What U-Factor is required for windows in California?
For prescriptive new single-family construction under the 2025 Energy Code, the maximum is generally 0.27 in Climate Zones 1–5, 11–14, and 16, and 0.30 in Zones 6–10 and 15. Project type, exceptions, and performance compliance can change the applicable value, so use the permitted CF1R.
Does every California climate zone require the same SHGC?
No. The new-construction prescriptive values are 0.23 in Climate Zones 2, 4, and 6–14; 0.20 in Zone 15; and not required in Zones 1, 3, 5, and 16. Even where no prescriptive maximum applies, solar comfort and energy modeling still deserve attention.
Does Title 24 apply to replacement windows?
Applicable alterations and replacement fenestration are covered, but the rules and exceptions are not identical to new construction. Confirm the permit scope and use the current alteration compliance documents rather than copying a new-home table.
Is Low-E glass automatically Title 24 compliant?
No. Low-E describes a coating technology. Compliance is based on the required whole-product performance and project documentation. Two Low-E products can have different U-Factor, SHGC, VT, color, and reflectivity.
Do sliding glass doors count as fenestration?
Yes. The CEC treats a door with at least 25% glazing as a fenestration product. Large sliders, folding glass doors, and pocket-door systems therefore need to be coordinated with the energy model and window schedule.
Are NFRC ratings required for custom windows?
NFRC-certified values are the clearest standard route for rating residential products. The code documents also identify default and alternative methods in specific situations. Your energy consultant and local building department should confirm the acceptable rating source for a custom system.
Can windows manufactured in China comply with Title 24?
They can, provided the exact proposed product has acceptable whole-system performance documentation, matches the approved project values, and meets all other applicable California and local requirements. A country-of-origin claim cannot replace product-specific evidence.
Does Title 24 cover wildfire, structural, and water requirements?
No. Part 6 focuses on energy performance. A California project may also need to address structural loads, safety glazing, egress, fall protection, water penetration, WUI or wildfire rules, acoustic goals, and local amendments. These checks should appear alongside—not inside—the energy review.
Let’s review the openings before they become expensive decisions.
Send us your floor plans, elevations, window schedule, or rough-opening dimensions. We can help you organize the product options, glass build-ups, finishes, and Shop Drawing questions for your California design team to review before production.
